A conventional method for preparing soybean milk includes cooking and grinding boiled soybeans, water-soaked raw soybeans or soybean powders, and then pressing the ground material. Since about one-third by weight of soybean feed is discarded as a solid residue or soybean milk residue in the conventional methods for preparing soybean milk and tofu. As a result, a large amount of nutritious and functional components of soybeans such as fibrous materials, lipids, amino acids and inorganic materials, etc. are lost from soybean foods as soybean milk residue.
Methods to overcome the problem of losing nutritious components, and prepare soybean milk containing the entire nutrients of soybeans (referred to as “whole soybean milk”) have been suggested, e.g., decomposing and treating the soybean milk residue with an enzyme (Korean Patent Laid-Open Publication No. 2001-41120); using a combination of ultrasonic and steam treatments (Korean Patent Nos. 41494 and 59907); and reducing the production of soybean milk residue with a high temperature/high pressure treatment (Korean Patent No. 86038), etc. However, most of the above methods are not suitable for commercialization because they tend to yield soybean milk containing large particles resulting in coarse texture or precipitation of the particles, which has a disagreeable taste or scent resulting from retreatment of the soybean milk residue. Particularly, the methods employing an enzymatic decomposition technique have not overcome a disadvantage of being non-economical because of the use of an expensive enzyme.
Further, methods such as one for preparing whole soybean milk using processed and treated raw soybean powders (Korean Patent No. 182829) have been reported, but they could not avoid the problem of losing some part of nutritious components in a pre-treatment process for processing soybeans to powders, and thus are not suitable for utilizing the entire nutrients of soybeans.
On the other hand, Korean Patent No. 822,165 discloses a method for preparing a whole soybean milk and tofu comprising the following steps. After soaking whole soybeans or dehulled soybeans in room temperature water for about 8-15 hours and subjecting them to the first grinding using a grinder (Crusher), a refining process to remove outer skin of soybeans or impurities in the ground liquid is carried out 1 to 3 times by a refiner. Then, the resulting liquid is subjected the second grinding using a fine grinder (Ultramizer), and the resulting ground liquid is maintained at 85 to 90° C. for 1 to 2 minutes to inactivate enzymes in the liquid. Next, it is micronized through ultra-high pressure homogenization process, to prepare a whole soybean milk. Alternatively, soybean liquid and soybean milk residue may be separated by a fluid separator, and the separated soybean milk residue may be mixed with purified water and recycled in a circulating grinding device for approximately 30 to 50 minutes at 50 to 60° C. to soften the liquid from the soybean milk residue. Then, a mixed solution of the soybean liquid separated by the liquid separator and the softened liquid from soybean milk residue circulated by the circulating grinding device is micronized through an ultra-high pressure homogenizing process, to prepare a whole soybean milk.
However, the above methods have a disadvantage that the soybean milk product shows viscosity increase and thickening phenomenon over time, which results in an unfavorable texture on tasting, and makes it impossible to have a long shelf life.
Accordingly, the present inventors have endeavored to develop an economical and efficient method for preparing a whole soybean milk which has small particle diameters and excellent long-term storage stability. It was discovered that a whole soybean milk having small particle diameters and showing almost no change in viscosity when stored for a long time can be prepared, by conducting cooking process of soybeans after roasting them, and micronizing particles in a cutting manner instead of a conventional mill stone method.